The magnetic disk drive is indispensable in today's advanced information society as a device capable of recording huge quantities of data which can also allow the data to be stably read and written. One example of such as magnetic disk drive is a hard disk drive (HDD), common in personal computers and massive server installations. The magnetic disk drive is typically constructed from a magnetic recording medium (magnetic disk) for recording data thereto, a magnetic head for reading and writing the data, and circuit modules, such as a voice coil motor for driving the head, a channel integrated circuit (IC), a pre-amplifier, etc.
The magnetic head comprises a write head for writing data and a read head for reading the data recorded on the magnetic disk. Recently, in order to achieve a higher recording density of the data on the magnetic disk, HDDs having an assist mechanism using microwaves and methods which drive the assist element synchronized to the write signal have been proposed. The magnetic head reads and writes while moving above the magnetic disk at an extremely low flying height. To control the flying height, typically, a technique is used to improve the reliability of the magnetic disk drive. In some prior art methods, the flying-height control function measures the output resolution of the read head and uses this to capture changes in the stationary flying height caused by changes in the air pressure or changes in the ambient temperature. In practice, the structure of the write head, the shape of the flying surface of the slider, and the suspension are designed to set the stationary flying height, which is in the specifications. However, when a high-frequency signal is written (in particular), the flying height decreases due to expansion caused by the heating of the write head (write protrusion), and the head comes into contact with the disk medium. As a result, more precise control is necessary because of concern about reduced reliability of the drive caused by repeated head contact with the disk medium.
Currently, a heating element, such as a thermal flying-height control (TFC) or dynamic flying-height control (DFC) for controlling the flying height of the slider by applying power and intentionally causing thermal expansion is installed in the magnetic head and is used in flying-height control. One method carries out the control by synchronizing this heater to the write gate (WG) signal. From the perspective of control synchronized to the write signal, another structure uses a write-safe circuit using the signal induced in the read path by the write signal in the write path.
However, in any of these methods, it becomes difficult for a magnetic head to write a signal on a magnetic recording medium because the write magnetic field strength generated by the write head is reduced. Consequently, the quality of the signal obtained is degraded. Thus, a stronger assist becomes necessary as the signal frequency increases. On the other hand, when a high-frequency signal is written, the concerns are contact with the medium caused by the lower flying height due to the expansion (write protrusion) caused by the heating of the write head, data loss, damage to the head, and a drop in the reliability of the drive. Normally, the flying height is controlled to correspond to the changes in frequency in the radial direction of the magnetic recording medium, but is not controlled in the circumferential direction. Thus, a concern is that intermittent contact develops in sections in the circumferential direction and the signal quality degrades as a consequence of this contact.